Process for producing french fries having an extended holding quality

ABSTRACT

A process for preparing frozen potato strips which remain crisp for an extended period of time after finish frying. Potatoes which have been cut into strips and blanched are contacted with an aqueous solution having a pH in the range of about 5.5 to 8.5 which contains a hydrolyzed starch product, such as dextrin or maltodextrin. The pH of the aqueous solution is maintained within the desired range by the addition thereto of a basic alkali salt. A conventional chelating agent and reducing sugar may also be included in the aqueous solution. After contact with the aqueous solution, such as by immersion, spraying, and the like, the potato strips may be partially dried in hot air and are then frozen. The frozen potato strips are prepared for consumption by finish frying under suitable time-temperature conditions. Contacting the blanched potato strips with an aqueous solution containing a hydrolyzed starch product and having a pH in the range of 5.5-8.5 results in the production of potato strips which upon finish frying have a strong potato flavor and a crisp surface with the finish fried strips retaining their crispness for an extended period of time.

This application is a continuation-in-part of application Ser. No.08/089,470, filed Jul. 12, 1993, now U.S. Pat. No. 5,302,410.

This invention relates to the production of frozen potato strips which,when finish fried for consumption, provide french fries having enhancedcommercial holding quality. More particularly, the invention relates toa process for producing blanched frozen potato strips which remain crispfor longer periods of time after finish frying in comparison withconventionally prepared french fries.

BACKGROUND OF THE INVENTION

French fried potato strips, commonly referred to as french fries, servedin most fast food restaurants and other food service institutions, arepurchased by the restaurant in bulk from commercial suppliers in theform of partially fried (par-fried) and frozen potato strips which arestored in frozen condition until shortly before serving. At that pointthe par-fried potato strips are prepared for consumption by finishfrying in fat or oil.

Procedures for producing such par-fried potato strips are well known inthe processed potato industry. Typically, raw potatoes are cut intostrips of desired size and blanched in steam or hot water to inactivateenzymes and partially cook the potatoes. The blanched strips usually arethen dehydrated to reduce their weight (as water) by up to 30% andpar-fried for 30 to 90 seconds at about 300°-400° F. (149°-204° C.), andthen frozen. In a preferred commercial procedure the blanched strips,prior to dehydration, are immersed in a dilute aqueous solutioncontaining a food grade sequestering agent, such as sodium acidpyrophosphate (SAPP) and a reducing sugar, such as dextrose or glucose.SAPP, present at a level of about 0.5% to 1.5%, minimizes productdiscoloration by chelating metal ions such as iron and copper present inthe processing water. Dextrose or other reducing sugar in the aqueoussolution facilitates uniform color development upon frying.

The use of frozen par-fried potato strips has been widely adopted infast food restaurants because of the convenience and savings in laborcosts they provide. However, par-fried potato strips presently availablesuffer from the disadvantage that when finish fried for consumption thefrench fries lose their desired crispness after a relatively shortperiod of time and become undesirably limp and soggy. Thus, while thefrench fries are crisp immediately upon removal from the fryer, theybecome limp and soggy within minutes after preparation due to themigration of internal moisture within the fried strips into the outersurface of the fries. Such limpness of the french fries results inobjectionable appearance, taste and texture and is a principal featureby which consumers identify a poor product.

Also, fast food restaurant operators maintain proper serving temperatureby holding the french fries under a heat lamp after finish frying.However, this tends to accelerate moisture migration, so that the frenchfries tend to even more rapidly become limp, chewy and soggy.

Suppliers of frozen par-fried potato strips have proposed a number ofsolutions in order to improve the crispness of french fries after finishfrying. For example, the surface treatment of potato strips with firmingagents such as calcium lactate, gums, alginates, high amylose starches,and other hydrocolloids has been suggested. However, these and otherproposed solutions neither fulfilled initial expectations nor have beenwidely accepted in the industry as a satisfactory solution to theproblem.

As an alternative to the use of frozen par-fried potato strips, somerestaurants and other food service institutions prefer to serve frenchfries prepared from potato strips which have not been subject to anintermediate par-frying step. For example, the french fries may beprepared from potato strips which are cut from whole potatoes on thepremises of the restaurant, with the freshly cut potato strips beingwashed and finish fried for consumption. Such french fries are perceivedto have a more desirable, "homemade" flavor than french fries preparedfrom par-fried potato strips. However, french fries prepared from potatostrips which are finish fried for consumption promptly after being cut,rapidly develop a limp and soggy texture after finish frying,particularly when held under a heat lamp. Despite any flavor preferencewhich may be provided by french fries prepared from freshly cut potatostrips, the rapid development of such objectionable texturecharacteristics is a significant disadvantage.

SUMMARY OF THE INVENTION

The present invention provides a process for the production of frozenpotato strips which, when finish fried for consumption, have enhancedcommercial holding quality. That is, the potato strips of thisinvention, upon finish frying, have a crisp surface layer and a mealyinner core and retain their surface crispness and rigidity for a longerperiod of time after finish frying than conventional french fries.

In accordance with one embodiment of the present invention, raw potatoesare washed, cut into strips of a desired size and blanched in accordancewith well-known procedures. Such procedures are exemplified in U.S. Pat.No. 4,254,153 to Ross et al. After blanching, the potato strips arecontacted with an aqueous solution having a pH in the range of about 5.5to 8.5 and which contains a hydrolyzed starch product, such as a dextrinor maltodextrin. The pH of the aqueous solution is adjusted to thedesired range by any suitable means, such as the addition of an ediblebasic alkali salt, preferably tetrasodium pyrophosphate (TSPP).Conventional ingredients including a sequestering agent such as SAPP,and a reducing sugar such as dextrose, glucose, etc., may also beincluded in the aqueous solution. After contact with the aqueoussolution, the strips may be partially dehydrated, after which they arepar-fried and frozen. It has been found that contacting the potatostrips with an aqueous solution containing a hydrolyzed starch andhaving a pH in the 5.5 to 8.5 range, after blanching and prior todehydration and par-frying of the potato strips produces potato stripswhich remain crisp for longer periods than conventional french frieseven when held under a heat lamp after finish frying. Thus, the frozenpar-fried potato strips are finish fried in a deep fat or oil bath for ashort period of time, such as 1.5 to 3.5 minutes at a temperature ofabout 300°-375° F. (149°-190° C.). The resulting french fries have asuperior texture and color and are characterized by a crisp surfacelayer and mealy inner core. In addition, the french fries thus preparedretain their crispness and rigidity for longer periods of time afterfinish frying, without becoming limp, chewy and soggy.

In accordance with another embodiment of the invention, potato stripsare frozen after contact with the aqueous hydrolyzed starch solutionhaving a pH in the 5.5 to 8.5 range, without being par-fried. Accordingto this embodiment, which is intended to produce french fries having astronger potato flavor than french fries produced from potato stripswhich have been par-fried, the potato strips are blanched, contactedwith the aqueous solution and frozen. Preferably the potato strips arepartially dehydrated after contact with the aqueous solution and priorto freezing. The frozen potato strips thus produced are prepared forconsumption by finish frying in a deep fat or oil bath for from about 4to 6 minutes, preferably about 4.5 to 5.5 minutes at 300°-375° F.(149°-190° C.), depending on the cut size of the potato strips. Thefinish fried strips of this embodiment have the strong potato flavor ofproduct prepared by finish frying of freshly cut potato strips, butretain desired crispness and rigidity for extended periods of time afterfinish frying.

DETAILED DESCRIPTION OF THE INVENTION

In the process of this invention, raw potatoes of a variety known to besuitable for preparing french fries, are washed, peeled and trimmed inaccordance with conventional practice and are cut into strips of adesired size and shape customarily used for french fries such asshoestring potato strips, crinkle-cut strips, and straight cut thickstrips. For example, the strips may have a width and thickness of fromabout 0.25 inch (6.35 mm) to about 0.5 inch (12.7 mm) and several inches(more than about 10 cm) in length. After cutting, the strips may bewashed to remove surface starch.

The potato strips thus prepared are blanched according to conventionalprocedures in order to inactivate enzymes and remove excess free sugarsfrom the surfaces of the cut strips. Typically the strips are blanchedby immersion in hot water at about 160° F.-210° F. (71°-99° C.) for 2-15minutes, with a temperature of 170° F.-190° F. (76°-88° C.) for 4-10minutes being preferred. Alternatively, the strips may be blanched insteam, at atmospheric pressure for about 2-10 minutes.

It has been found that the crispness and rigidity of finish fried potatostrips are improved by contacting the blanched strips, beforepar-frying, with an aqueous solution containing a hydrolyzed starchproduct, such as dextrin or maltodextrin, with the solution having a pHin the range of about 5.5 to 8.5 such as by the addition of an ediblebasic alkali salt. The inclusion of a hydrolyzed starch product such asdextrin and maltodextrin in the aqueous solution at a concentration ofbetween about 1%-12% by weight, provides a thin coating or glaze on thepotato strips which promotes increased crispness of the potato stripswhen finish fried. At such levels the hydrolyzed starch product iseasily dispersed in water and forms a clear thin solution having aviscosity approximately the same as water. Higher levels may be used butare not preferred, since at higher concentrations the surface of thepotato strips become slightly tacky upon finish frying which promotesundesirable clumping of the potato strips. Hydrolyzed starch products,including dextrins and maltodextrins, used in the aqueous solution havea Dextrose Equivalent (DE) value of from about 2 to about 10. The DEvalue is a measure of the reducing equivalence of the hydrolyzed starchproduct referenced to dextrose and expressed as a percent (dry basis).The higher the DE value, the more reducing sugars are present and thegreater the amount of browning which occurs in frying. Hydrolyzed starchproducts having a DE value of higher than about 12 promote theproduction of unacceptably dark french fries upon finish frying.Preferably a maltodextrin such as corn maltodextrin and potatomaltodextrin are used as the hydrolyzed starch product in the aqueoussolution. Suitable maltodextrins include potato maltodextrins from AvebeAmerica and corn maltodextrins from A.E. Staley Mfg. Co.

The aqueous solution with which the blanched potato strips are contactedhas a pH in the range of between about 5.5 to 8.5, preferably betweenabout 6.5 and 7.0. Contacting the blanched potato strips with theaqueous solution having a pH in this range results in a slight"sloughing" of the surfaces of the potato strips providing french friesexhibiting a substantial increase in crispness, rigidity and stand-upafter finish frying. While the inclusion of a hydrolyzed starch productalone in the aqueous solution provides some increased crispness,adjusting the pH of the aqueous solution to the 5.5 to 8.5 range incombination with the hydrolyzed starch product provides an unexpectedlygreater increase in crispness of the potato strips upon finish frying.The use of an aqueous solution having a pH above about 8.5 providesfurther increase in the crispness of the french fries but is generallynot desirable since such a high pH results in unacceptable mottling,increased sloughing, and unacceptable flavor in the potato strips afterfinish frying.

The pH of the aqueous solution is adjusted to the 5.5 to 8.5 range bythe addition of an edible basic alkali salt to the solution. Any basicalkali salt which is suitable for use in food products in the amountrequired to adjust the pH of the aqueous solution to the desired rangemay be used. Suitable basic alkali salts include alkali metalpolyphosphates, such as tetrasodium pyrophosphate (TSPP), NaOH and thelike. The use of TSPP as the basic alkali salt is generally preferred.

The amount of alkali salt included in the aqueous solution will, ofcourse, depend on the specific alkali salt used, the particular pHdesired, and other materials, if any, included in the solution, and canbe readily determined by routine experimentation. For example, the useof 0.5% to 1.0% SAPP as a conventional chelating agent in the aqueoussolution will provide the solution with a pH of about 5.0 to 5.3. Theaddition of TSPP (pH 9.2) to the aqueous solution in an amount of from0.2% to 0.6% by weight will increase the pH of the aqueous solution tothe desired range. When SAPP is included in the aqueous solution as achelating agent and TSPP is added as the alkali salt, the pyrophosphatemoiety, P₂ O₇, in the aqueous solution preferably should not exceedabout 1.5% by weight, for at higher levels undesirable off-flavors aredeveloped in the french fries.

Any conventional chelating or sequestering agent and reducing sugarcommonly used in treating blanched potato strips may be used in theaqueous solution of this invention. Thus, sodium acid pyrophosphate(SAPP) or other suitable and effective food grade chelating orsequestering agent may be included in the aqueous solution, in order tominimize product discoloration due to inorganic ions in the processingwater. If SAPP is used, it is usually present in amounts of about 0.2%to 1.5% by weight. Similarly, a reducing sugar such as dextrose, glucoseand the like may, if desired, also be included in the aqueous solutionto facilitate uniform browning of the strips upon finish frying. Ifused, reducing sugar is present in the aqueous solution in amounts up toabout 1.0% by weight.

The aqueous solution is maintained at a temperature of between about130° F. to 180° F.(54° C.-71° C.) when contacted with the blanchedpotato strips. Preferably the blanched strips are immersed in theaqueous solution by passing the strips through a dip tank containing theaqueous solution for a period of time ranging from a few seconds toseveral minutes, preferably from about 10-60 seconds. However, otherprocedures such as spraying or contacting in a transfer trough may alsobe used.

After contact with the aqueous solution the potato strips are drainedand preferably are then partially dehydrated to reduce their moisturecontent. Any of the conventional drying procedures used in theproduction of frozen par-fried potato strips may be used, such as, forexample, subjecting the potato strips to heated air having a temperatureof from about 100° F. to 350° F. (38° C. to 177° C.) for from about 2 to20 minutes in order to reduce the moisture content of the strips to thepoint at which the strips have lost about 5% to 25% of their initialweight.

Thereafter, the partially dehydrated strips are par-fried by immersingthem in a deep fat fryer for a short period of time, for example, 20 to90 seconds at a fat temperature of about 325° F.-390° F.(162° C.-199°C.). Par-frying removes additional moisture from the strips so that uponcompletion of par-frying, the potato strips have a solids content ofbetween about 30%-40%.

After par-frying, the potato strips are frozen, packaged and shipped orstored for subsequent use. To prepare the par-fried strips forconsumption, they are finish fried in a deep fat or oil bath at atemperature of from about 300° F. to 375° F. (149° C. to 190° C.) for1.5 to 3.5 minutes to develop color and crispness. The potato strips,after finish frying, have a crisp outer surface which is golden brown incolor, a fluffy interior and increased holding quality or "stand-up"when compared to conventionally prepared french fries. The finish friedpotato strips of this invention remain crisp for a longer period of timewhen held under a heat lamp after finish frying.

While the invention has been particularly described with respect tofinish frying of the frozen par-fried potato strips, it will beunderstood that potato strips which have been processed in accordancewith the present invention and par-fried may, if desired, be preparedfor consumption by other conventional procedures such as, for example,oven baking and microwave heating.

If desired, the potato strips may be treated in accordance with thepresent invention and frozen without being par-fried. That is, potatostrips are blanched and contacted with an aqueous solution containing ahydrolyzed starch product, such as dextrin or maltodextrin, having a DEvalue of less than about 12, and an edible basic alkali salt, such asTSPP, to provide the solution with a pH in the range of about 5.5 to8.5, as described hereinabove. The concentration of hydrolyzed starchproduct in the aqueous solution may be from about 1% to 12% by weight.After contact with the aqueous solution the potato strips preferably arepartially dehydrated to effect a weight loss of between 5% to 25%, afterwhich the potato strips are frozen. To reconstitute the frozen stripsfor consumption they are finish fried in a deep fat or oil bath at atemperature of between 300° F. to 375° F. (149° C. to 190° C.). Sincethe frozen strips which have not been par-fried have a higher moisturecontent than par-fried strips, they are finished fried for a slightlylonger period of time, typically 4 to 6 minutes, and preferably betweenabout 4.5 to 5.5 minutes. The specific time-temperature conditions forfinish frying the frozen strips are, of course, a function of the cutsize of the potato strips, and can be readily determined by thoseskilled in the art. The resulting finish fried potato strips have astrong potato flavor comparable to french fries prepared form freshlycut potato strips, but retain crispness after finish frying forsubstantially longer periods than french fries prepared from freshly cutpotatoes which have not been contacted with the aqueous solution of thisinvention.

The following examples are intended to illustrate, but not to limit, thepresent invention. Unless otherwise indicated, all parts and percentagesare by weight.

EXAMPLE I

A random sample of Russet Burbank potatoes having an average solidscontent of 20.7% was washed, peeled, trimmed and cut into 5/16×5/16 inch(7.9×7.9 mm) strips and blanched in hot water at 180° F. (85° C.) for8.5 minutes. After blanching, the potato strips were immersed for 40seconds in an aqueous solution having a temperature of 160° F. (71° C.),with the aqueous solution containing the following ingredients:

    ______________________________________                                        Ingredient          Weight Percent                                            ______________________________________                                        Sodium Acid Pyrophosphate                                                                         0.5%                                                      Tetrasodium pyrophosphate                                                                         0.5%                                                      Potato maltodextrin (DE of 6)                                                                     7.0%                                                      ______________________________________                                    

After removal from the aqueous solution the potato strips were drainedand then partially dehydrated in a conventional air dryer at 212° (100°C.) for 15 minutes. The strips were then par-fried for 51 seconds at370° F. (188° C.) and frozen. The par-fried strips were finish fried inhot oil at 350° F. (177° C.) for 2.75 minutes. Upon removal from thefinish fryer the potato strips were golden brown in color, with a crispouter surface and a fluffy interior. After finish frying, the potatostrips were held under a standard heat lamp at a distance of 18 inches(46 cm) from the heat lamp for 5 minutes at which time the texture ofthe french fries was evaluated.

A control sample of french fries was run for comparison purposes. Thecontrol sample was processed in an identical manner as that set outabove with the exception that the aqueous solution in which the blanchedstrips were immersed contained 0.5% SAPP and 0.3% dextrose, but notetrasodium pyrophosphate or maltodextrin.

Both the control sample and the sample produced in accordance with thepresent invention were evaluated for color immediately after finishfrying, and for crispness and stand-up after the finished fried stripshad been held for 5-7 minutes under the heat lamp. Color was measuredusing an Agtron reflectance colorimeter in which a higher readingindicates a lighter color. Crispness and stand-up were determinedsubjectively by personnel experienced in evaluating french fry quality.The results of these determinations are set out below in the Table.

                  TABLE                                                           ______________________________________                                               Color                                                                  Sample (Agtron Reading)                                                                           Evaluation Comments                                       ______________________________________                                        Control                                                                              66.9         Acceptable crispness, tenderness                          Invention                                                                            63.3         Shell more crispy than control                                                sample; better "stand-up" under                                               heat lamp than control                                    ______________________________________                                    

EXAMPLE II

This example illustrates the improvement in crispness retention offrench fries which are frozen without having been par-fried.

A random sample of Russett Burbank potatoes (specific gravity of 1.086)was washed, peeled, trimmed and cut into strips 5/16×5/16 inch (7.9×7.9mm.) and water blanched for 9 minutes at 175° F. (80° C.). Afterblanching, the potato strips were dipped in an aqueous solutioncontaining 0.4% sodium and pyrophosphate, 0.4% tetrasodiumpyrophosphate, and 3.0% potato maltodextrin (DE of 6) for 40 seconds at160° F. (71° C.). After removal from the aqueous solution the potatostrips were drained and partially dehydrated in a conventional air drierat 100° C. for 5 minutes to effect a weight loss of 10%. The strips werethen cooled with ambient moving air for 2 minutes and frozen for 10minutes at -22° C.

To provide a basis for comparison, a control sample of french fries wasproduced in the identical manner as that set out above, with the soleexception that the aqueous solution in which the blanched strips wereimmersed contained 0.5% sodium acid pyrophosphate and 0.4% dextrose, butno tetrasodium pyrophosphate or maltodextrin.

Two pounds of both the french fries produced by the process of thepresent invention and the control sample were finish fried at 350° F.(177° C.) for 4.5 minutes, held under a heat lamp for 2 minutes, andwere then evaluated for flavor and crispness. The control sample had astrong potato flavor but the french fried potato strips had very littlecrispness, with the strips tending to be limp and soggy, after the 2minute hold under the heat lamp. The samples of the present inventionalso had a strong potato flavor and retained moderate crispness for 5 to6 minutes after removal from the heat lamp. These results confirm thatthe process of this invention significantly increases the holding timeof blanched frozen french fries which have not been par-fried.

What is claimed is:
 1. A process for producing frozen potato stripswhich remain crisp for an extended time after finish frying whichconsists essentially ofcutting potatoes to produce elongated potatostrips, blanching the potato strips, contacting the blanched potatostrips with an aqueous solution having a pH in the range of about 5.5 to8.5 which contains between about 1% to 12% by weight of a hydrolyzedstarch product having a DE value of less than 12, and then freezing thepotato strips without the strips having been par-fried, whereby thefrozen strips when finish fried have a crisp surface and a mealyinternal texture, with the surface of the strips remaining crisp for anextended period of time after finish frying.
 2. The process defined inclaim 1 in which the hydrolyzed starch product is selected from thegroup consisting of dextrins and maltodextrins having a DE value of from2 to
 10. 3. The process defined in claim 2 in which the hydrolyzedstarch product is potato maltodextrin.
 4. The process defined in claim 1in which a basic alkali salt is included in the aqueous solution in anamount sufficient to provide the aqueous solution with a pH in the rangeof about 5.5 to 8.5.
 5. The process defined in claim 4 in which thebasic alkali salt is selected from the group consisting of alkali metalpolyphosphates.
 6. The process defined in claim 4 in which the basicalkali salt is tetrasodium pyrophosphate.
 7. The process defined inclaim 1 in which the aqueous solution contains from 1% to 12% ofmaltodextrin, from 0% to 0.5% of a reducing sugar, from 0% to 1.5% of asequestering agent and tetrasodium pyrophosphate in an amount sufficientto provide the aqueous solution with a pH of about 6.5 to 7.5.
 8. Theprocess defined in claim 7 in which the sequestering agent is sodiumacid pyrophosphate and the tetrasodium pyrophosphate is present in anamount of from 0.2% to 0.6% by weight of the solution, with the totallevel of pyrophosphate moiety in the aqueous solution being not morethan about 1.5% by weight.
 9. The process defined in claim 1 in whichthe blanched potato strips are immersed in the aqueous solution, whichis at a temperature of between about 130° F. to 180° F.(56° C. to 83°C.), for between 2 seconds to 3 minutes.
 10. The process defined inclaim 1 in which the potato strips are blanched in hot water at 160° F.to 210° F. (71° C. to 99° C.) for 2-15 minutes.
 11. The process definedin claim 1 in which the strips are partially dehydrated after contactwith the aqueous solution by contacting the potato strips with heatedair having a temperature of about 100° F. to 350° F. (38° C. to 177° C.)for from 2 to 20 minutes.
 12. A method of improving the crispness offrench fried potato strips prepared by finish frying of blanched, frozenpotato strips without the strips having been par-fried which consistsessentially ofcontacting blanched potato strips with an aqueous solutionhaving a pH in the range of about 5.5 to 8.5 which contains betweenabout 1% to 12% by weight of a hydrolyzed starch product having a DEvalue of 2 to 10, and thereafter freezing the potato strips, whereby thefrozen strips when finish fried have a crisp surface and a mealyinternal texture, with the surface of the strips remaining crisp for anextended period of time after finish frying.